Disease

[FLT3_HUMAN] Defects in FLT3 are a cause of acute myelogenous leukemia (AML) [MIM:601626]. AML is a malignant disease in which hematopoietic precursors are arrested in an early stage of development. Note=Somatic mutations that lead to constitutive activation of FLT3 are frequent in AML patients. These mutations fall into two classes, the most common being in-frame internal tandem duplications of variable length in the juxtamembrane region that disrupt the normal regulation of the kinase activity. Likewise, point mutations in the activation loop of the kinase domain can result in a constitutively activated kinase.[1][2][3][4][5][6][7][8]

Function

[FLT3L_HUMAN] Stimulates the proliferation of early hematopoietic cells by activating FLT3. Synergizes well with a number of other colony stimulating factors and interleukins. [FLT3_HUMAN] Tyrosine-protein kinase that acts as cell-surface receptor for the cytokine FLT3LG and regulates differentiation, proliferation and survival of hematopoietic progenitor cells and of dendritic cells. Promotes phosphorylation of SHC1 and AKT1, and activation of the downstream effector MTOR. Promotes activation of RAS signaling and phosphorylation of downstream kinases, including MAPK1/ERK2 and/or MAPK3/ERK1. Promotes phosphorylation of FES, FER, PTPN6/SHP, PTPN11/SHP-2, PLCG1, and STAT5A and/or STAT5B. Activation of wild-type FLT3 causes only marginal activation of STAT5A or STAT5B. Mutations that cause constitutive kinase activity promote cell proliferation and resistance to apoptosis via the activation of multiple signaling pathways.[9][10][11][12][13][14][15][16][17][18][19]

Publication Abstract from PubMed

The class-III receptor tyrosine kinase (RTKIII) Flt3 and its cytokine ligand (FL) play central roles in hematopoiesis and the immune system, by establishing signaling cascades crucial for the development and homeostasis of hematopoietic progenitors and antigen-presenting dendritic cells. However, Flt3 is also one of the most frequently mutated receptors in hematological malignancies and is currently a major prognostic factor and clinical target for acute myeloid leukemia (AML). Here, we report the structural basis for the Flt3 ligand-receptor complex and unveil an unanticipated extracellular assembly unlike any other RTKIII/V complex characterized to date. FL induces dimerization of Flt3 via a remarkably compact binding epitope localized at the tip of extracellular domain 3 of Flt3, and invokes a ternary complex devoid of homotypic receptor interactions. Comparisons of Flt3 with homologous receptors and available mutagenesis data for FL have allowed us to rationalize the unique features of the Flt3 extracellular assembly. Furthermore, thermodynamic dissection of complex formation points to a pronounced enthalpically-driven binding event coupled to an entropic penalty. Together, our data suggest that the high-affinity Flt3-FL complex is driven in part by a single preformed binding epitope on FL reminiscent of a 'lock-and-key' binding mode, thereby setting the stage for antagonist design.